1. Field of the Invention
The present invention relates to a new polyamine, a process for its preparation and its use as epoxy resin hardener.
2. Discussion of the Background
Polyamines, especially diamines, on the one hand have acquired prominent importance as starting components for the preparation of polyamides, and on the other hand are widely employed for curing epoxy resins especially those based on bisphenol A.
While low molecular weight polyamines are readily accessible industrially and a large selection is therefore available, the problem of preparation of higher molecular weight di- and polyamines has not yet been solved satisfactorily.
A process which has been known for a long time for the preparation of such tailor-made polyamines comprises reacting NCO prepolymers with amino alcohols, the NH.sub.2 group of which is protected from the NCO group in the form of an aldimine or ketimine group, and then hydrolyzing the product. In this process, it is important for the amino group to be separated from the OH group by at least 6 C atoms, since if the two groups are closer together, 5-, 6- and 7-membered rings can be formed and the desired Schiff base are obtained only as a byproduct. It has therefore not been possible to date, for amino alcohols in which the functional groups are 2-4 C atoms apart to be employed for the preparation of polyamines.
The object of the present invention was therefore to provide a simple, reproducible process for the preparation of higher molecular weight di- and polyamines.
Surprisingly, it has been found in parallel that certain amino alcohols, in which the functional groups are separated from one another by 4 C atoms, do not give a heterocyclic 7-membered ring with aldehydes and ketones, as expected, but give azomethines (Schiff bases) if the amino alcohol is the compound 3-aminomethyl-3,5,5-trimethyl cyclohexanol: ##STR4## A separate Application DE P 43 11 901.8 of the same priority relates to these Schiff bases.
In achieving the object, it has been possible to prepare high molecular weight di- and polyamines in a simple manner by reaction of the above Schiff base and diisocyanate prepolymers (adducts of diisocyanates with polyols or trimers of diisocyanates) and subsequent hydrolysis.